US 1411700 A
Description (OCR text may contain errors)
w. T. HOLMES AND G. H. WHITTINGHAM.
' MOTOR CONTROLLER- I APPLICATION FILED FEB. 8,1918- 1,41 1,700. 7 ed Apr. 4, 1922.
2 $HEETSSHE ET l- W. T. HOLMES AND G. H. WH-ITTINGHAM.
APPLICATION FILED FEB. a, 1918.
Patented Apr. 4, 1922.-
2 SHEETSSHEET 2.
UNITED STATES ,j-PATENT OFFICE 7 WILLIAM r. HOLMES, or summons, AND (manor. nwmr'rrnem, Q's-3mm" PABLJILRYLAND, ASSIGNORS TO MONITOR MORE, A CORPORATION 01 MARYLAND. v
comaomna conrm or num- To all whom z'tmagr] concem:
' Be it known. that we, WILLIAM T. Homms and Gnonon H. Wm'rnncH M, cltizens of the United States, residing at Baltimore,
Mar land, and Bancroft Park, in the county of altimore and State of Maryland, re-
spectively, have invented certain new' and useful Improvements in Motor Controllers, of which the following-is a specification.
Where direct current electric. motors are employed for'work requiring frequent reg versal of the motor, it. is common to provide the motor with a dynamic brake circuit for causing the motor to quickly slow down prior to reversal of the current in the, armature circuit of the'motor; In order to ut1+ lize the dynamic brake," it is, necessary td; maintain the field strength of the motor 'fora'time sufiicient, at least, topermit the motor with its load to slow down. This is. usually accomplished by keeping the shunt field wind- 'ing of the motor. connected to the supply circuit, thus maintaining a permanent field.
There are occasions, however, due to various conditions on the line or in the ower station, when the voltage on the supp y 'circuit drop considerably or fails entirely, and in such cases the motor field becomes weakened or de-energized and the dynamic brake fails towork, and injury to the machinery operated by the motor results. Thus, inthe operation of large planet's, where the otor reverses at the end of each movement of theplaner table, if a dynamic brake depended upon to slow the motor down ,prior to reversal, and the potential of the" supply circuit fails, the braking action also 'failsand' injuryto the plianermechan'ism is liable to The purpose of the present invention is to provide means whereby, if the voltage of the supply circuit falls below a pro-determined point,or fails entirely, orif the motor is purposelydisconnected from the sup ply circuit, the field'of the motor will, nevertheless, be ener ized from an independent source for a su cient length oftime to permit the dynamic brake to act. In carrying out our invention, we provide a small dynamo electric machine, preferably a small shunt wound motor, which willoperate as a generator, and connect the armature of this nerator in parallel with'the shunt field of t e work motor to the supply circuit; and
' allow thegenerator to run idly a motor.
Specification of Letters 2mm, :Pa tenmd Apr, 4, Application filed. February 8, 1918. Serial No. 218,982. I i
If, for any reason, the voltage of the su ply circuit at the terminals of the shunt fie d of the work motor falls considerably,- or
entirely fails, the idle motor, by reasonof its inertia, will continue to run as a enerator and supply current to the shunt old of the work motor for a suflicient time to permit the latter to generate its own brak- We also .held -1n' its closed position, while the ma.-
v M rovide a switch, which, 1n 1ts. closed :pOSltlOIl connects the-- chine'sare in operation, by'a voltage magnet havingits' windings connected across the supply circuit, but upon a pre-determined dropin voltage in the supply circuit the magnet releases the switch, which opens automatically, preferably disconnecting both i the work motor and generator from the supply circuit and closing the dynamic brake.
circuit. It is desirable that the switch should 'openinstantly and close the dynamic brake circuitiif the voltage of the supply .circuit" -fai ls;- but as the terminals of the generator are connected to the supply cir-Y ,cuit directly .or through the switch andhe ce to the terminals of the magnet, the
current generated bythe generator will cirv culate through the magnetcoils and cause the latter to. hold the switch in closed position for a time if the "electro-motive force of the generator approximates the normal "line voltage. In order to avoid this continv gency, we proportion the magnet so that it will release the switch upon a pre-deter-' mined dro in voltage -'on the line, and we provide s cient' resistance in' the armature circuit of the generator to prevent it from generating a counter E. M. F, equal to the minimum voltage required at the terminals of the magnet to hold the switch closed.
Preferably, we supply the generator with a' .fiy wheel in order that it may have sufiicient inertia to continue operatlng as a generator, after being disconnected [from the supply circuit, long enough to energize the field'of the main or working motor while the latter with its load-is slowing down.
- In the accompanying drawing, 7 Fig. 1 is a diagrammatic view illustrating i The switch S supply circuit-upon failure of voltage.
Referring to l! ig. 1 of the drawing, L and 'L indicate the supply wires leading from asuitahle currentscnircc, and A indicates the working motor comprising the armature a, and shunt li'eld windii'ig 71. The motor is shown counaictcd to the supply circuit through a switch S. and a reversing switch R, for rswersing the direction of current tliu 'ijmgh the motor armature, is also shown. comprises stationary contacts 1 and 2, which are connected directly to the su iiply wires by conductors 3 and 4;. The conductor 3 also leads to contact 5 of the reversing switch, and the conductor :tleacls to contacts 6 and 7 of the reversing switch,
The switch S is also shown with two contacts, 8 and 9, which are connected by conductors 10 and 11 to the arms 12 and 13, re-
spectively, of-the reversing switch. A hold- 'ing magnet M is provided for holding the switch S in its closed position, as shown in the drawing, and this magnet has high resistanceicoils connected at one end to the supply wire L by conductor 14, and at the other end to supply wire L by conductor 15. The magnet is proportioned so that it v will hold the switch in closed position so long as the potential on the line orv supply circuit is normal and until the potential falls to a predetermined amount, say 20%, below the normal, when the magnet will release the switch arm 8, andsaid arm will drop and open the switch. The switch arm is pro vided with contacts 16, 17, 18, and 19, adapt ed to engage the fixed contacts 1, 8, 9, and 2,.
respectively, when the switch is closed. When the switch arm drops open, the engagement between these several contacts is broken and the contact 18 then engages a contact 20 in the dynamic brake circuit of the motor. i.
The shunt field f of the work motor A is connected, as shown, by conductors 21 and 22 to movable contacts 16 and 19, respec- .tively, on the switch arm '8, and when said arm is closed, this field is connected to the supply circuit through contacts 1 and 2 and conductors" 3 and 4. lVhen the switch S is open, the shunt field f is dis-engaged from the supply circuit. One brushof the armature a of the work motor is connected by conductors 23 and 24 through starter to the movable contact 17 oi the switch S, and
. the other brush of said armature is connected by conductor 26 to the movable contact 18 on the switch S. When the switch S is versed, as
closed, the contacts 17 and 18 are connected to the supply circuit through the reversing switch. In the position in. which the arms of the reversing switch are shown in the drawing, "the contact 17 is connected to side L of the supply circuit through conductor 10, arm 12,'contact and conductor 4;", and the contact 18 is connected to the side L through contact 9, conductorll, switch arm 13, contact 5, and conductor 3". :iollowingthe circuits just traced, it will be evident that in the position in which the reversing switch arms, are shown, when the switch S is closed, current will flow from the side L of the supply circuit through conductors 1, 10, 24L, starter 25, and conductor 23 to thearmature a, and thence through conductors 26,11, and 3?, to the side L of the supply circuit. Vhen the reversing switch arms are swung to the right, the arm 13 will engage the contact, 6 and the arm 12 will engage the contact 5, and the direction of current through the armature a will be rewill be obvious without tracing the circuits further.
The dynamic brake circuit of the motor A extends from one brush of said motor through conductors 23 and 23 to a brake resistance 27 thence through conductors 28 and 29 to the contact 20. From the conductor 29 a branch conductor 29* leads to the contact 30 on the reversing switch midway between the contacts 5 and 6.
hen the switch S is open, the dynamic brake circuit is closed at the contacts 18 and 20, that is, the circuitof the armature a is then closed upon itself through the brake resistance 27. The switch S, however, is always held in its upper or closed position,
while the motor is in operation and the volt-' age on the line L, L is normal, and the dynamic brake circuit is only closed at the contacts 18 and 20 when the voltage drops sufiiciently to cause the magnet M to release the switch arm 8. v
The reversing switch is ordinarily operated automatically by the machine which the motor drives. Thus, in the operation of a planer, a tappet on the planer. table maybe used to operate the reversing switch near the completion of each movement of the table. As the reversing switch is moved from the position shown in the drawing over to the right hand position, it first dis-connects the armature a from the supply circuit and then the arm, 13 engages the contact 30 and closes the dynamic brake circuit at this int, causing the motor to slow down. he arm 13 .then interrupts the, dynamic brake circuit and moves on to the contact 6 while the arm 12 engages the contact 5 and 'the current from the supply circuit is then directed through 'the armature a in the reverse direction. Similarly, when the reversing switch arms are moved from right to left, the connection to the supply circuit is first broken, then the dynamic brake circuit is made up andbroken, and then the armature is connected to the supply circuit and the current flows in the opposite direction through the armature. 'Thus, there is a braking action before each reversal of the current in the armature circuit. The reversin switch is shownconventionallyr In practice, it will be understood that this switch will be arranged so that the dwell of the arm 13 on the contact 30 will be for a sufficient length of time to allow the full braking eflect to take place.
So long as the voltage on the line is normal, the switch S remains closed and the field winding f :of the work motorremains connected to the supply circuit and receives full "voltage. In case of failure of voltage on jthe line, however, or a lar e drop in voltage, if the field f remaine connected to the line, it would be de-energized or .so weakened that the armature a would not generate the necessary braking current to slow down the motor upon the operation of the. reversing switch. To overcome this difficulty, upon a pre-determined drop in voltage or failure of voltage on the line, the magnet M' releases the switch arm 8 and the armature and shunt field circuits of the motor A are thereby automatically dis-connec ted from the supply circuit and thereuponthe dynamic brake circuit is closed at thecontacts 18 and 20, and the field f is ener- 1gized from a separate source until the motor as been slowed down by its'own dynamic braking action. This separate source of current for the field comprises a small exciter E, which may be, and preferably is, a relativelysmall shunt wound motor comprising 'an'armature a and a-shunt field winding' f, the armature circuit of'this small.
motor being connected through conductors 31 and 32 to the terminals of the field f of the work motor A, and thence to. the/switch contacts 16 and 19, by conductors 2 "and22,
respectively. Whenthe switch S is closed,
it will-be evident that the field fjof the work motor and the armature. a,- of the small ex: citer will be connected in parallel with one another-and to the source of'supply. The
field f of the machine Evis also connected to the supply circuit by way of conductors 31-32.' Preferably, the armature of the machine E is provided with a fly wheel 9,
in order that the armature may have considerable inertia, to .kee the machinein operation after the circults have been dis-' connected from the supply circuit.
It will be evident that while the main motor A is running with the switch S closed, the dynamo electric machine E will also operate as a motor, and the operation of the latter will not beafi'ected by the movements of the reversing switch; but u on failure of voltage in the supply circuit, 0th machines will be-immediately dis-connected from said circuit by the opening of the switch S, and
the machine E, then actin as a generator, Wlll furnish current at suitable voltage to keep the field f energized while the main motor A is coming to. a stop through the action of the. dynamic brake, the brake circuit bein then closed at the contacts 1'8 andof the motor would be kept open at thecontacts 18 and 29', so that the dynamicbrake could not act. sistance 33 is placed in series with the armature of the machine E to cut downthe voltage supplied by it to the terminals of the magnet M to the point where the current supplied by said machine will not cause the magnet to support the switch arm. Thus, if the magnet is proportioned so that it will release the switch arm upon a drop of 20% in the voltage of the supply circuit,
the voltage. supplied by the machine E at the terminals of the magnet coils should .be at least 20% lower than the normal line voltage, and this is regulated by placing the external resistance 33 in the armature circuit. of the machine E, or the machine, which is I small, may be wound with sufficient internal resistance for the purpose. This resistance,
either internal or external, is also necessary are connected through the.
To prevent this, a dead re"-.
in order to prevent injury to the machine I when it. is started as a motor.' Of course,
the voltage supplied by the machine E at the terminals of the shunt field coil f of the motor A .will be less than the line voltage, but suflicient to maintaina strong field during the braking action; Q
' t willbe seen that the generator E will run continuously and idly as a motor so long as conditions on the supply circuit are normal, and that it is only in case of abnormal conditions resulting in failure of voltage in the suppl circuit, or a very considera le drop in v0 tage, that this idle running motor becomes a generator and supplies current to the field of the working motor. A motor-driven generator, operated from the Supply circuit, might be fprfiployed for sup-' ply ng current to the of the work motor, after failure of voltage on the supply circuit; but an ordinary shunt wound motor is also a satisfactory generator and we prefer to use it as a means for exciting the field of the main motor when the voltage on the supply circuit fails.
are shownconnected directly to the supply circuit, with the exception of the armature circuit of the work motor which is connected through the electromagnetic'ally controlled switch to the supply circuit. It is not necessary to the operation of the-invention that any of, the connections tq the 'su ply circuit shall be broken, upon failure voltage,
except the armature circuit of the work thence through contact motor, which must be' broken, in order to close; the dynamic brake circuit.
'In Fig. 2 the idle motor or generator d of the supply is connecte to the side L circuit by conductor and to the side L by conductor 36, and the shunt field f of the work motor is shown connected to said conductors 35 and 36. Thus, said shunt field is connected to the terminals of the generator E, and said shunt field and generator are connected in parallel with one another directly to the supply circuit. The switch S is shown in the osition which it occupies when. the-line vol motor is in operation. In this position, the armature a of the work motor receives current from the side L of the supply circuit through conductor 37 to fixed contact .38, 39 on the switch, and thence through the metal part 40 of the switch arm to the armature conductor 41, thence through the armature to conductor 42, thencethrough starter 25 and conductor 43 to insulated contact 44 on the switch,
and thence through stationary switch contact 45 and conductor 46 to the side L of the supply circuit. The switch S is held in its closed position, while the voltage is normal, by the magnet M having its coils connected by conductors 47 and 48 to supply L, respectively. When the switch S opens, upon failure of voltage, the contact 40 on the switch arm engages the contact 49 of the dynamic brake circuitf 'As I .shown, this contact is connected by connec'ted by conductor 41 to the metal ductor 50,'through brake resistance 27 and conductor 42 to one brush of .the armature a. 'The other brush of said armature is conpart 40 of the switch arm, on which the contact 39 is secured, and hence, when the contact 39 is in engagement with the contact 49 the armature will be on a closed circuit which includes the brake resistance. In this position of the arm, the connection between the supply circuit and the armature will be bro en at the contacts 38 and 45. In the conductor 36 is arranged a sistance 51,which is normal shunted throu switch arms 8.
rotective rey brid ed or h a. switch operated ythe As shown, a conductor 52 leads from the conductor 36 at a point be- 7 fixed contact 53,
rent to the field 7, long enou the dynamic brake to act.
, lt.1S not cut of? tage is normal and the,
generator but this resistance short-clrcuited through the switch and is generator, by the tween the armature of the small generator E and the protective resistance 51, to the which is en aged by a contact 54 on the switch arm. nother stationary contact 55 engages theucontact 54 and this contact 55 is connected by conductors 56 and 46 to the supply wire L. when the switch is closed, the protective -re sistance 51 is shunted; but when the switch drops open the resistance 51 is in series with the armature of. the small generator.
In operation, while the line voltage is normal, the switch S- remains closed, as shown in the drawin Upon failure of voltage, the magnet hf releases the switch arm, which closes the dynam c brake circuit. The generator E which runs idly as a motor when the switch is closed, operates as a' generator when the switch is opened and supplies curith the idle motor or generator connected directly to the supply circuit as shown in' Fig. 2, so that therefrom when the voltage fails, the generator might be short-circuited through other translatin devices on the supply circuit, which would be left connected thereto upon failure of volta e. In order to prevent this occurrence, t e protective resistance 51 is provided in series with the thrown in series with the opening ofthe switch, only in case of failure of volta e or such a sudden drop in voltage as would cause the magnet M to release the switch arm.
What we claim is:
1. The combination with a motor having a shunt field winding, of a supply circuit, a dynamic brake circuit, switching mechanism adapted, in one position, to connect the armature of the circuit, and in another position to close the dynamic brake circuit, a retaining device adapted to hold the mentioned position while the voltage in the supply circuit is normal and to release the mechanism and cause the closure of the brake circuit when the voltage drops to a predetermined value below normal, and means for supplying current to the shunt field of said motor, independentl of the supply circuit, at a pressure insu cient to revent the magnet from releasing the switc when the line voltage falls to said predetermined value. g 2. The combination with a motor having a shunt field winding, of a supply circuit, a dynamic brake circuit, a switch adapted, in one position, to connect the armature of the motor to the su other position to c ose the dynamic brake circuit-,a magnet, connected to the supply motor to the supply I mechanism in the first Thus, I
.80 drops to open position and as h to allow is normally ply circuit, and in aniao' circuit, adapted to hold the switch in the first mentioned position while the voltage inthe supply circuit is normal and to release the switch andcause' the closure of 5 the brake circuitiwhen the voltagedrops to a. predetermined value below normal, and a.
generator, normally. operated idly from the supply circuit, adapted to supply currenta to the shunt field of said motor at a ressure insuflicient to prevent .said magnet mm 10 releasing-the switch when the line voltage